1. Field
The present invention finds application in the field of electrical safety devices and in particular relates to an electronically operated safety switch.
2. Brief Description
Safety switches designed to be applied to barriers and panels for protection of machines and industrial plants comprise a casing designed to be anchored to a fixed part of the protection and housing thereinside the electrical and electronic switching components for connecting the switch to the plants to be controlled.
Instead, an operating element designed to interact with the switch to open/close one or more circuits connected to the switch itself at the opening and closing of the panel or other moving part is fixed in correspondence of the door or opening panel of the protection.
In this way, the activation of the controlled plant is made possible only if the protection is in safe state with the panel closed, when there is interaction between the switching portion and the operating element.
In this context, the switches of greater diffusion provide an interaction between the mobile actuator and the circuit portion contained in the fixed casing through a slot in the casing.
Through this slot it will be possible to insert a suitably shaped actuator, e.g. a key, to act on an locking/unlocking mechanism for suitable contacts housed in the casing, as disclosed for example in U.S. Pat. No. 7,456,368 and in DE10056458.
Some of these switches are provided, close to the actuator, of a centering element which serves mainly to recover the possible misalignment between the slot of the casing and the actuator. Similar switches are disclosed in U.S. Pat. No. 7,563,995 and EP2112674.
These switches, even if relatively reliable, have some operative drawbacks, especially because of the possibility that dust or dirt creep into the slot, in addition to presenting safety problems.
As matter of fact, the particular configuration of the slot makes it possible to insert thereinto, due to a negligent or fraudulent conduct, a different actuator similar to the one in charge associated with the movable part of the protection, being able to cause a not safe restart of the system even in a condition of open protection.
For these reasons, most recent solutions involve the replacement of the mechanical actuators with electronic and encoded actuators which provide the use of transponder devices, for example of the Radio Frequency Identification type (RFID) that make possible the communication between the fixed part and the movable part of the switch, allowing the mutual recognition and activation of the system only in a safe condition.
For example, U.S. Pat. No. 7,775,072 discloses a switch provided with a movable portion anchored to the door of a security barrier and provided with an actuator with one end designed to be inserted in a recess made in the fixed portion of the switch.
The end of the actuator is also provided with a transponder adapted to communicate with a detection circuit placed in the recess when the distance between the elements reaches a minimum value, for signaling the correct closure of the door. The movable portion houses thereinside a locking element which interacts with the actuator and keeps it in the closed position, being able to be removed only after the operation of a piston actuated by a command sent via the detection circuit.
US2011/0259060 discloses a switch similar to that described above and in which there is an actuator of the key type provided at one end with a transponder adapted to be detected by a sensor housed in the fixed part of the switch, in which a block element is also housed.
WO2013/087 183 discloses a safety switch having a box-shaped casing provided both with a slot adapted to receive an key actuator provided with mechanical coding, in particular a solenoid, and a proximity sensor adapted to communicate with the actuator to detect its position.
These latter types of switches, while ensuring greater reliability and safety, are however affected by some drawbacks.
For example, in this last case the switch is still of essentially mechanical type, with a key actuator that acts on a kinematic mechanism connected to traditional switching means. The proximity sensor has the sole purpose of detecting the presence of the actuator for generating a presence signal, to enable the switching means.
However, the lock of the actuator in the closed position is always entrusted to the mechanical elements, inherently unsafe.
Moreover, the connection between the proximity sensor and the switching means is realized by wires located externally to the case defining both an encumbrance and a potential risk due to a possible contact with the actuator.
A further drawback of these switches is represented by the fact that the known actuators of the transponder type or other electronic detection system do not guarantee a sufficiently precise alignment between the antenna or transmitter and the reader or receiver, so that there may be an absence of communication even in the closed condition of the protection, with consequent lack of operation of the system.
Furthermore, the known switches have a low flexible configuration that does not allow the application to the protection according to a plurality of orientations, so as to be able to adapt to the various possible methods of opening of the protection.